Method for the manufacture of the fuse head element of electric fuses



M. HARMS ETAL 3,421,210 HOD FOR THE MANUFACTURE OF THE FUSE HEAD Jan. 14, 1969 MET ELEMENT OF ELECTRIC FUSES Flled Aug 2, 1965 mamfioooooooooooouo CEECECE m m 3 m m g m ww m fi fi m my Qkm\mv Em United States Patent 3,421,210 METHOD FOR THE MANUFACTURE OF THE FUSE HEAD ELEMENT 0F ELECTRIC FUSES Maximilian Harms, Hannover, Germany, and Gustav Allan Wetterholm, Gyttorp, Sweden, assignors to Nitroglycerin Aktiebolaget, Gyttorp, Sweden, a company of Sweden Filed Aug. 2, 1965, Ser. No. 476,304 Claims priority, applicatigr/l Sweden, Aug. 5, 1964,

us. c1. 29-623 1m. (11.110111 69/02 1 Claim ABSTRACT OF THE DISCLOSURE The present invention relates to an improved method for the manufacture of fuse head elements used in electric fuses, which elements include two conductive posts arranged side by side and secured in relation to each other by means of an insulated strap, one end of said conductive posts being bridged by an electric incandescent Wire which in turn is embedded in a priming material, in which method a strip of the conductive material is stamped out along a portion of its width in such a way that the posts are left securely seated in pairs in the remaining portion of the strip, the strap being also produced and the incandescent wires attached in conjunction therewith.

Such a method is already known. In this connection, there are obtained pairwise seated posts connected by a strap as an intermediate product. Further treatment requires this strip to be cut into decimeter long sections which are mounted in a carrying device in straight tracks or grooves arranged in the same. The unit thus obtained, accommodating only some hundred fuses, is used for the continued treatment, i.e. dipping, drying, gauging. From the manufacturing aspect, this method can hardly be considered logical due to the amount of manual labour involved.

It has been proved that this disadvantage can be removed or substantially reduced if the strip of conductive material obtained from the stamping operation is rather rolled into a spiral form having a space between the coils, in large lengths including e.g. SOD-3,000 pairs of posts together with straps and incandescent wires, and is fixed in this condition, after which the priming material is applied by dipping in the usual way.

According to a particularly suitable embodiment of the invention, in which the strip of conductive material is made from a strip of iron plate or some other magnetic material, the cut lengths together with the securely seated posts, straps and incandescent wires can be fixed to a magnetic carrier body, after which the ends of the posts are dipped into a bath of a liquid priming material. Said fixing process can, however, also be attained in another Way, e.g. so that the cut-out strip lengths, when in coil form, are secured in a recess in a carrier body, after which process dipping is carried out.

According to another embodiment of the invention, a spacing member can be arranged between various loops of the conductive strip. The spacing member may take the form of a hose or the like. The task of such a member is to prevent posts, associated with various loops, from coming too close to each other during handling of the carrier body, so that subsequent to the dipping process the priming material bridges the posts of adjacent loops in an unintentional manner.

It is usual to roll the stamped-out strip in a circular coil form. However, there is nothing to prevent the strip from being rolled in some other Way, e.g. so that the loops take an oval shape.

The method according to the invention is advantageous insomuch that it makes it possible to sort accepted fuses from non-accepted fuses in a rational manner. It is possible, for this purpose, to rejoin the long, spirally wound units by means of spot welding or brazing so that an endless belt is obtained. This belt is then fed to an automatic gauging device where it can be decided, based on their resistance, whether individual fuse head elements are acceptable or not.

The invention will now be described in the following with reference to the attached drawing which shows, in more detail, the stages of the various working operations up to the finished fuse.

FIG. 1 shows, in side view, the stages undergone in producing a substance for a fuse head element,

FIG. 2 shows a diagrammatic view of a length of a coiled, stamped-out strip,

FIG. 3 shows diagrammatically how the priming material is applied by means of dipping, and

FIG. 4 shows a side view of the completed fuse head element.

As can be seen from FIG. 1, the process of stampingout the fuse-head element blank from a metal strip is carried out in six different stages. In the first stage the strip is stamped out in such a way that it forms three rows of holes, the holes 2 in the first row being circular and the function of which being to enable the transport of the strip. The holes 3 in the second row take the form of slits lying at right angles to the strip and the holes 4 in the third row also take the form of slits in the same direction although they are somewhat shorter. Seen across the width of the strip, one hole in each row lies opposite the other. In the longitudinal direction of the strip two slits 5 having a cut-away portion in each slit, are stamped out on both sides of the holes 3 in the centre row, said cut-away portions on slits 5 being turned towards the slits 3. Each pair of slits 5 and 3 are intended to form the live part of a finished pair of posts which are to be surrounded by a strap. The slits 4 should lie between two posts and are made in order to facilitate working of the metal strip. The next stage consists of applying a plastic strip 6 on both sides of the metal strip 1 at the same height as the intermediate row of holes 3, 5 in such a way that both the strips are secured to each other by means of cross pieces passing through the holes 3, 5. Both the plastic strips are intended to form blanks for a strap which is to surround and secure two posts in relation to each other.

In both the subsequent stages the metal strip 1 is further stamped out so that the ends 7 of each pair of posts are formed and a slit 8 is dispoesd between the remaining sections of said posts which are not to be surrounded by the strap. In the next step the end 7 of eachpost leg is bent at right angles to the directional plane, after which a Wire 9 of resistant material is caused to engage the folded part of each post. The end section of each post is then unfolded so that the resistor wire is clamped securely in said posts. In the next step the metal strip 1 as well as both the plastic strips 6 are stamped out resulting in the formation of a narrower strip 10 having a pair of posts 11, strap 12 and incandescent thread 13, secured to the same. A good electric contact between incandescent wire and posts is ensured by welding said wire into the posts. This operation is not shown on the drawing. According to the invention the strip 10 is now cut up into large lengths containing a large number of post pairs having straps and incandescent wires, and coiled up into spiral form as can be seen from FIG. 2. The coiled strip-lengths 14 are now mounted in a magnetic carrier body 15 having a handle 16, after which the end of each post is dipped into a bath 17 containing priming element so that a drop is formed and which is seated on the incandescent wire 13. On completion of the dipping process, the strip lengths are dried and the formed fuses are cleaned. The fuse head element comprising two posts 11, a strap 12 and an incandescent thread 13 and a primer can now preferably, subsequent to being gauged for resistance in the incandescent wire, be cut away from the strip. A finished fuse head element is shown in FIG. 4, the same designations being used for the various sections as in FIG. 1. The formed fuse head is given the reference numeral 14a.

What we claim is:

1. A method for manufacturing fuse head elements of electric fuses, which comprises:

(a) stamping a strip of magnetic and a conductive material out along a portion of its width so that a plurality of parallel pairs of posts of conductive and magnetic material are left securely seated in the re maining portion of the strip,

(b) each of said pairs being secured in relation to each other by means of an insulated strap,

(c) bridging the upper ends of each member of a pair of posts with an electric incandescent wire,

(d) cutting said strip of material into lengths that contain between about 500 and 3,000 pairs of posts that have straps and incandescent wires attached to the same,

(e) rolling up each length into a spiral form,

(f) maintaining a minimum clearance between adjacent loops of the spiral,

(g) attaching the spiral form in a fixed positional relationship to a magnetic carrier body,

(h) immersing the ends of the posts that have the incandescent wire attached thereto in a bath of priming material,

(i) removing said posts from said bath so as to allow the priming material bridging each post of a pair of posts to solidify, and

(j) detaching the spiral form from said magnetic carrier body.

References Cited UNITED STATES PATENTS Re. 11,589 2/1897 Donnelly 14459 1,407,157 2/1922 Jessen 29-623 X 1,777,916 10/1930 Schaffer-Glossl 29623 X 2,671,451 3/1954 Bolger 335-285 X 2,747,257 5/ 1956 Ashcroft et al 29--623 3,184,655 5/1965 Brown 335-285 3,320,564 5/1967 Sosey et al 335-285 JOHN F. CAMPBELL, Primary Examiner.

I. L. CLINE, Assistant Examiner. 

